(1) Field of the Invention
The present invention relates to a fabricated, refractory metal core and a method of using such a core for casting cooling passages. More specifically, this invention relates to a method of incorporating a refractory metal core comprised of movable tabs and base body into the casting process so as to provide a cast part with cooling passages and form definition.
(2) Description of Related Art
Several refractory metals including molybdenum (Mo) and Tungsten (W) have melting points that are in excess of typical casting temperatures of nickel and cobalt based superalloys. These refractory metals can be produced in wrought thin sheet or formed in sizes necessary to make cooling channels characteristic of those found in turbine and combustor cooling designs and other applications. Thin refractory metal sheets and foils possess enough ductility to allow bending and forming into complex shapes. To increase ductility, sheets and foils may be elevated in temperature. The ductility yields a robust design capable of surviving a waxing/shelling/casting cycle.
Since cooling channels formed from refractory metals provide for the dissipation and/or removal of heat in operative parts incorporating such channels, it is often times advantageous to provide the surface of such operative parts with a pattern of holes extending into the part from the outside or inside through the thickness of the part by which heat may be dissipated by accommodating cooling flow. Such a pattern of holes may be accomplished through post-processing operations including the laser drilling of cooling holes. Cooling channel/hole recast attributed to laser drilling and Electrical Discharge Machining (EDM) can contribute to premature crack formation and reduced durability/life. In addition, it is difficult to vary the cross-sectional geometry of the cooling passages created by such drilling. Because different regions of an operative part may experience different forces and heating properties, it would be preferable to be able to vary the cross-sectional geometries of the cooling passages drilled into different regions of a part.
In addition, the complex shapes of many parts result in regions which can prove difficult or impossible to reach by drilling and are therefore difficult to provide meaningful cooling presently. Such regions include, but are not limited to, spaces between attachment studs/hooks and the exposed surface of combustor panels, near rails, component edges, and grommets.
Also, tailored cooling is desirable. In addition to the potential for increased cooling efficiency, such tailoring provides the ability to tailor aerodynamic performance.
There therefore exists a need for a method of using refractory metal cores to cast parts possessing a surface pattern of cooling channels or holes through which heat may be dissipated. Ideally, the cross-sectional geometry of such holes should be configurable so that the heat dissipation and aerodynamic performance qualities of the holes generally correspond to the requirements of their location on a part. In addition, there exists a need to deposit such cooling channels in locations on a part whose geometry precludes drilling such holes.
Accordingly, it is an object of the present invention to provide a method for casting cooling passages in workpieces.
It is an additional object of the present invention to provide a base core for use in casting cooling passages into workpieces.
In accordance with the present invention, a method for casting a workpiece comprises the steps of applying a protective coating to a base core the base core comprising, a metal strip comprising a generally planar expanse, a plurality of tabs arranged in a repeating pattern upon the metal strip each of the tabs comprising a base end, a terminus end, and a tab shaft extending from the base end to the terminus end wherein each of the tabs is angularly displaceable about each base end of the tabs, injecting a molding substance about the tabs of the base core, encapsulating the base core in a shell, removing the molding substance, casting about the base core, and removing the base core.
In accordance with the present invention, a base core for use in casting cooling passages in a workpiece comprises a metal strip comprising a generally planar expanse, a plurality of tabs arranged in a pattern upon the metal strip each of the tabs comprising, a base end, a terminus end, and a tab shaft extending from the base end to the terminus end, wherein each of the tabs is capable of independent angular displacement about each the base end of the tabs and wherein the base core is bent to form a hard back core.